This inventionn relates generally to electro-acoustic transducers and, in particular, to a transducer in which a transducer plate carrying a piezo-electric layer is clamped between two bearing members along an annular edge region of the transducer plate.
Piezo-electric transducers are well known in the prior art. In this type of transducer, acoustic pressure causes extremely small deflections of a transducer plate. The transducer plate typically carries a piezo-electric layer in which an electric voltage is created at electrodes connected to opposite sides thereof when the layer is subjected to the acoustic pressure. The electric voltage thereby created is proportional to the acoustic pressure. For example, when sound waves impinge upon the transducer plate and piezo-electric layer, a time varying voltage representative of the sound wave appears on the electrodes of the piezo-electric layer. Inversely, a deflection of the transducer plate can be achieved when an electric voltage is applied across the piezo-electric layer attached to the transducer plate.
Since the electric voltage in the acoustic field is usually an alternating voltage, an electrical connection between the electrodes and the electrical components on a housing for the transducer is subjected to mechanical stresses transmitted from the transducer plate. For this reason, the electrical connection has typically been formed from small electrically conductive bands which are then attached to the electrical components on the housing. As a result of the small thin bands which are required to avoid placing any undue mechanical influence on the transducer plate, the electrical connection is exposed to an increased risk of breaking, which in turn leads to loss of functionability of the transducer. In order to avoid this difficulty, one prior art solution has been to utilize a conductive rubber to establish an electrical connection with electrodes of the piezo-electric layer. The conductor rubber therefore lies immediately against the electrodes. Moreover, the conductive rubber can also function as one of the bearing members which supports the transducer plate. Typically, only one subsection of the bearing member is electrically conductive.
As is known, the frequency behavior of the transducer is directly influenced by the bearing used for the transducer plate. Thus, the type and shape of the bearing member is critical to the operation of the transducer. Thus, the edge region of the transducer plate is generally seated between elastic bearing members of a very specific shape and elasticity. Many years of testing with a great variety of bearing members have lead to the result that a bearing member having two annular, concentric shoulders of elastic material is desirable, these bearing members may comprise triangular trapezoidal cross section.
If conductive rubber were then utilized for contacting the electrodes, the selection of the bearing members is extremely restricted. Furthermore, conductive rubber is generally composed of strip shaped bands. A specific, annular fashioning of such conductive rubber for employment as a bearing member for transducers is very expensive to manufacture, since the contacting of the electrodes must be undertaken galvanically on both sides of the piezo-ceramic. The conductive rubber, therefore, would have to be joined of two pieces and could only be conductive in specific regions.
The present invention overcomes these drawbacks in the prior art.